Justification:
This species is listed as Endangered based on a small population size and continuing decline driven primarily by hunting and habitat loss. It is estimated that there are less than 2,500 mature individuals remaining in the wild, and the population is expected to undergone a decline of at least 20% over the next 2 generations (24 years) due to continued hunting pressure across the range.

A poorly known howler monkey, its range has been elucidated recently through the efforts of the Centro de Proteção de Primatas Brasileiros of the Instituto Chico Mendes de Conservação da Biodiversidade, Paraíba (Oliveira et al. 2004). It occurs along coastal north-east Brazil in three states: Maranhão, Piauí and Ceará. The type locality is Miritiba, now called Humberto de Campos, on the coast of Maranhão, which it would seem marks the western limit to the range, just east of Rio Itapecurú. Besides the type locality, Bonvicino et al. (1989) mapped Boa Vista, just east of the lower Rio Parnaíba in Maranhão (locality 9, map Figure 2, Table 2); Goiabeira, Granja (locality 5) near the coast on the left (west) bank of the mouth of the Rio Coreaú in Ceará, and Bom Jardim, São Benedito (locality 4) in the Serra da Ibiapaba. Oliveira et al. (2004) indicated the Serra da Ibiapaba as the eastern limit to the species’ range. Guedes et al. (2000) registred two further localities in the Serra da Ibiapaba in the municipality Ibiapina. Oliveira et al. (2004; pers. comm.) have found that it occurs further south than was previously recognized, extending at least to the Rio Poti in Piauí.

There is no information available on population densities, but total population size is undoubtedly small due to the extreme destruction and fragmentation of its forests in a very restricted geographic range.

In Maranhão, they are found in open, transitional babaçu palm forest (Gregorin 2006). The Serra da Ibiapaba, a humid forest enclave (brejo nordestino), has humid forest on its eastern slopes (that remains only because the terrain is so steep). Oliveira et al. (2004) report that in Ceará (Viçosa do Ceará and Coreaú) they are also found in areas of semideciduous and dry forest.

The howler monkeys are the large leaf-eaters of the South American primate communities. The molar teeth are particularly adapted for their chewing leaves through shearing. They spend up to 70% of their day lying and sitting about quietly among the branches, fermenting leaves in their enlarged caecums. Like the spider monkeys, they are prehensile-tailed, with a naked patch of skin on the under surface at the tip. Their most characteristic feature is the deep jaw which surrounds the enlarged larynx and hyoid apparatus, a resonating chamber. It is with this enlarged and highly specialized voice box that they produce their howls (grunts, roars and barks). Howling sessions, usually involving the entire group, can be heard particularly in the early morning and are audible at distances of 1-2 kms (Drubbel and Gautier 1993).

Howlers are the only New World primates which regularly include mature leaves in their diet, although softer, less fibrous, young leaves are preferred when they are available. Their folivory and ability to eat mature leaves is undoubtedly one of the keys to their wide distribution and the wide variety of vegetation types they inhabit. Mature fruit is the other important food item, especially wild figs (Ficus) in many regions, but they also eat leaf petioles, buds, flowers (sometimes seasonally very important), seeds, moss, stems and twigs, and termitaria. Red howler groups are usually small, ranging in size from 2-16 animals and averaging 4-10 (Neville et al. 1988). Alouatta ululata groups generally comprise four or five or up to 11 or so individuals.

Oestrus lasts 2-4 days, with intervals between oestrous periods of about 17 days. Interbirth intervals are generally about 16.6 months, although they may be shortened by the death of an infant to about 10.5 months (Crockett and Sekulic 1984).

Very few populations still survive in a region which has a long history of human occupation, and resulting high levels of forest loss and hunting. The species survives only on hill tops and steep slopes, where they are inaccessible to hunters and where the forest is protected by law (Areas of Permanent Preservation according to the Brazilian Forest Code (Law 4.771, 15 September 1965).